Apparatus for gas plating



Dec. 27, 1955 o. F. DAVIS ETAL APPARATUS FOR GAS PLATING 2 Sheets-Sheet1 Original Filed July 14, 1949 am LP QV mm .msmmss INVENTORS OL/VER FDAV/5 HANS G. BEL/7'2 ATTORNEYS 1955 o. F. DAVIS ETAL 2,728,321

APPARATUS FOR GAS PLATING Original Filed July 14, 1949 2 Sheets-Sheet 2INVENTORS OL/VER F DAV/5 HANS 6. BEL/7'2 l I 3 m N w T u x I T15 a M 6 4n n u n 2 2r Q s m v C F: o L w l.

ATTORNEYS United States Patent O APPARATUS FOR GAS PLATING Oliver F.Davis, Troy, and Hans G. Belitz, Dayton, Ohio, assignors to TheCommonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation ofOhio Original application July 14, 1949, Serial No. 104,754. Divided andthis application October 8, 1952, Serial No. 313,738

1 Claim. (Cl. 11849) This invention relates to the art of deposition ofmetals. More particularly it relates to coating of metal bases. Stillmore particularly it relates to the plating of objects by the depositionof metal from readily decomposed volatile metal bearing compounds andapparatus for carrying out the process. 1

Depositing of thin film of metals, such as iron, nickel, cobalt, uponmetal bases has been accomplished in the past by enclosing an object tobe plated in a chamber sealed against entry of air. a

The chamber was purged with carbon dioxide and the object heated to atemperature at which volatile metal carbonyls decompose.

Following this a metal carbonyl gas was carbureted into a stream ofcarbon dioxide to form a dilute carbonyl medium which was metered intothe chamber. Upon coming in contact with the hot metal the carbonyl wasdecomposed and the metal component deposited.

This application is a division of Serial No. 104,754 of Davis et al.,filed July 14, 1949, now U. S. Patent No. 2,619,433.

This process has many'disadvantages which limit its usefulness. Whilethe chamber isfilled with a mixture of inert gas and metal carbonylvapors, plating only occurs when the carbonyl vapor contacts the hotobject and general decomposition may take place, with the result thatpowdered metal accumulates in the bottom of the chamber.

Further, the deposition rate is very slow and the process requires hoursto build up an appreciable depth of metal coating. In addition, thecoatings are brittle and adhered poorly to the base metal.

In another process, utilizing quite similar equipment, the brittlenessand poor adhesion has been largely overcome. In this process the metaldeposition is carried out in two stages.

After a thin layer of metal subjected to heat treatment at a temperatureof between 500 and 800 F. to expel the occluded gases. The object wasthen returned to the chamber and a second coating of the desiredthickness over the first layer deposited thereon.

This process, while producing adhering metal coatings, is still a timeconsuming one. It also requires that the plating cycle be interruptedwith consequent loss of materials due to purging the equipment to avoidformation of exposives mixtures of carbonyl gases with air.

It is an object of this invention to overcome the limitations anddisadvantages of the above described apparatus and processes. 7

it is another object of this invention to provide an apparatus forgaseous plating processes in which the time is deposited the object isfor depositing any thickness of coating is markedly shorter thanheretofore.

lt is another object of this invention to produce thicker adheringcoatings than have been produced heretofore. It is another object ofthis invention to provide an improved apparatus for carrying out theprocess wherein the metal carbonyl is not brought into the reaction zonein a dilute weak plating vapor state.

It is another object to provide an apparatus wherein the gaseous platingprocess may be operated under either positive or negative pressureconditions.

It is a further object of this invention to provide an apparatus foreffecting gaseous plating wherein the decomposition gases are quicklyremoved from the plating area to eliminate contamination of thedeposited metal film.

It is a still further object of this invention to provide an apparatusandprocess for continuous and rapid deposition of bright metal coatingsby directing the decomposable metal material to the metal surface.

It is still a further object of this invention to provide a simplifiedmethod and apparatus for depositing metal from a volatile metal compoundby continuously decomposing the compound an conducting the gaseousproduct resultant from the decomposition away from contact with hotmetal in order to avoid decontamination and dulling of the brightdeposit.

It is still another object of this invention to provide an apparatus forgaseous plating wherein the decomposable material is not brought up to adecomposition temperature before it is in the direct plating zone.

Other and more specific objects and advantages will be apparent to oneskilled in the art as the following description proceeds:

In this new apparatus provision is made whereby the plating compositionis introduced into the deposition chamber as a liquid instead of a gas.In this way it is possible to concentrate the stream of metal bearingmaterial at the heated surface.

The atomsphere in the neighborhood of the surface to be coated is thusmade up merely of fresh liquid propelled with force by the gas blastinto which deposition zone and encountering mainly the hot gaseousdecomposition products which are being removed as, for example, by suction' or vacuum drawn on the chamber.

This invention makes it possible to utilize metal carbonyls, alsonitroxyl compounds, nitrosyl carbonyls, metal hydrides, metal alkyls,metal halides, metal carbonyl halogens, and the like, which are eitherliquids at normal temperature and pressure conditions, or gasescompressible to liquid under any commercial feasible tem peratureconditions or solids convertible to liquids at temperatures below thedecomposition temperature of the compound, or to utilize solutions ofcarbonyls in volatile solvents such as petroleum ether.

Useful metals which may be deposited from the metallic carbonylcompounds are nickel, iron, chromium, molybdenum, tungsten, cobalt,telluriurn, rhenium, and the like.

Illustrative compounds of the other groups are nitroxyls, such as coppernitroxyl, nitrosyl carbonyls, for example, cobalt nitrosyl carbonyl,hydrides, such as tellurium hydride, gelenium hydride, antimony hydride,tin hydride, chromium hydride, the mixed organo metallo hydrides such asdimethyl alumino hydride, metal alkyls such as tetraethyl, lead, metalhalides such as rhodium carbonyl chloride, osmium carbonyl bromide,rhuthenium carbonyl chloride, and the like.

When introducing the liquid products into the closed chamber, the liquidis broken up into a fine spray by a blast of inert gas. Apparatus ofthis type usually delivers the liquid to the orifice through a centralpipe.

The inert gas is usually fed to the mixing point through an annularchamber surrounding the central pipe. The quantity of liquid atomized iscontrolled by adjustment of the orifice area. Commercial equipment, suchas fog nozzles or fine spray nozzles, such as the DeVilbis paint spraygun, can be readily adapted for use as the spraying means.

Carbon dioxide, helium, nitrogen, hydrogen, the gaseous product ofcontrolled burning of hydrocarbon gases free of oxygen, mixtures ofthese gases, and the like, have been utilized as the gas blast.

We prefer to utilize gas held under pressure of between 30 and 90 poundsper square inch for blasting, but the pressure range is subject to muchwider variation, depending upon the quantity of liquid being sprayed,the throw required from the nozzle to the plating surface, and so forth.

The throw distance between nozzle and plating surface is somewhatcritical in order to convert the liquid to a gas at a point in closeproximity to the plating surface. What this distance may be is readilydeterminable for any particular combination of liquid, temperature ofthe blasting gas and temperature of the plating object, fineness of thespray, and so forth. However, in view of the many ways in which theconditions may be varied, it will be seen that an exact number of incheswould only apply to specific conditions, and that the critical thingreally is that the liquid not impinge on the plating surface as a strongliquid spray.

Each material from which a metal may be plated has a temperature atwhich decompositions is complete. However, decomposition may take placeslowly at a lower temperature or while the vapors are being raised intemperature through some particular range. For example, nickel carbonylcompletely decomposes at a temperature in the range of 375 F. to 400 F.However, nickel carbonyl starts to decompose slowly at about 175 F., andtherefore, decomposition continues during the time of heating from 200F. to 380 F. A large number of the metal carbonyls and hydrides may beefiectively and efficiently decomposed at a temperature in the range of350 F. to 450 F. When working with most carbonyls we prefer to operatein a temperature range of 375 F. to 425 F.

It will be seen thus that the present invention is marl:- edly superiorto the processes utilized heretofore, because it accomplishes all of itsdecomposition quickly in close proximity to the heated surface area andbecause the liquid when converted to a vapor is then decomposed withoutdelay as the carbonyl or uitrosyl or hydride compounds come in contactwith the hot object to be plated.

Maintenance of the metal objects at temperatures in the generaloperating range is easily accomplished with numerous heating means, suchas radiant heating, electrical resistance heating, induction, and thelike.

The material to be decomposed is readily brought to the decompositiontemperature by atomizing the liquid with hot inert gas. The fine sprayof liquid can thus be transformed from say 100 F. to temperatures ofbetween 200 F. and 300 F. in a fraction of a second and the liquidconverted to a gas.

This transformation to a gas takes place in the vicinity of the hotobject to be plated, giving the process excellent integration forobtaining efficient operation.

Preparatory to coating base material he metal strip or object to beplated may be cleaned by employing the conventional methods used in theart, comprising electrochemically cleaning by moving the same through abath of alkali or acid electrolyte, wherein the strip is made to cathodeor anode.

Pickling of the metal with hydrochloric, sulfuric, or nitric acid, or acombination of acids, may also be made as a part of the cleaning processand the strip thoroughly rised or washed and dried prior to introductioninto the plating apparatus of this invention.

The apparatus of the invention and its use will be more readilyunderstood from a description of the process with reference to theapparatus and the specific examples.

in the drawings:

Figure 1 is a vertical sectional view showing diagram- 4 matically oneembodiment of the apparatus of this invention;

Figure 2 is a vertical section view of the apparatus taken substantiallyon the line 2-2 of Figure 1 and looking in the direction of the arrows;and

Figure 3 is a vertical sectional view along the line 3-3 of Figure 1.

Referring to the drawings in detail, there is shown an object 10 whichmay be a stationary positioned object or a moving sheet or the like. Theobject here shown is illustrated as stationary and suspended from asupport 11. Adjacent the object is a support 12 from which is suspendedsuitable heating means 13, suclias an electrical resistance coil maskedwith a suitable covering 14 which prevents plating on the heatingelement.

Supports 11 and 12 are secured in the wall of an air tight chamber 15.This chamber is provided with an aperture 16 for introduction andremoval of objects to be plated. The aperture 16 is fitted withreleasable closure means 17 rendered air tight by a suitable gasket 18.

Surrounding the chamber 15 is a metal jacket 19 having therein a closedspace 20 through which a suitable medium, such as water, may becirculated. The space 20 is shown in communication with an inlet 21 andan outlet 22.

It" pressure above atmospheric pressure is to be maintained in thechamber 15, an inert gas may be introduced by suitable means 25, such asa fan or blower.

Blower 25 is shown taking suction on a surge tank supplied with gas froma storage tank as indicated and introducing the gas at the chamber inlet27.

If pressures below atmospheric are to be maintained the chamber outletpipe 26a communicating with the chamber through outlet 26 may beconnected at the point indicated at 26b with a vacuum pump or exhaustfan. The exhausted gases which are a mixture of inert gas and carbonmonoxide may, if desired, be scrubbed to remove inert gas such ascarbon-dioxide, and the purified carbon monoxide returned to a metalcarbonyl generator to conserve carbon monoxide.

Liquid is introduced into the chamber through the rightwardly wall 28 ofchamber 15 by suitable spray means 30. Spray means 30 consists of acentral liquid tube 31 connected to a source of liquid 32.

The tube 31 is surrounded by a tube 33 mounted with a laterallyadjustable head 34, adapted with an external gear 35. Gear 35 isactuated by a gear 36 attached to a rod 37 which extends through asealed bushing 38 to a manually operable position outside the chamber15.

Tube 33 is connected to a suitable source of inert gas 39 through pipe40. Chamber 15 is provided with a suitable window 42 more completelyshown in Figure 3. This window comprises an inner pane 43 of glass orclear resin joined in air tight seal to the chamber 15 by suitablegasket means 44. The gasketing also seals tightly to an outer glass pane45 to form between said panes an air pocket 46.

This arrangement provides a clear view of the plating and sprayadjustment apparatus without danger of carbonmonoxide leakage to thearea where operators might be stationed.

In Figure 2 there is also shown a thermometer 48 suitably sealed in thewall of chamber 15 and the jacket t9 and extending outside the platingchamber for visual observation.

Conditions of operation of the apparatus in carrying out the processduring specific plating operations will be more readily understood fromthe following examples:

Example 1 Aluminum discs may be suspended from the support 11. Thechamber may then be sealed and purged of air by passing carbon dioxidegas therethrough. When the chamber 15 is purged the discs may be heatedby conduction due to intimate contact with resistance heater 13. At thistime the water may be started circulating in jacket 19 to maintain thechamber at a cool non-plating temperature.

When the thermometer 48 records temperature in the vicinity of the discsat approximately 390 F., nickel carbonyl may be introduced into thechamber by spray means 30. This nickel carbonyl may be under a pressureof about 50 pounds per square inch and sprayed at the rate of about 2pounds of nickel carbonyl per minute.

The spraying means may be carbon dioxide maintained under pressure ofabout 75 pounds per square inch. The decomposition of nickel carbonylproduces 4 volumes of carbon monoxide gas for each molecular weight ofliquid introduced. The gases may be removed by an exhaust fan whichmaintains a pressure in the chamber of between 1 and 2 inches of Hvacuum.

Under these conditions small discs may be plated to a thickness of manyhundredths of an inch in a matter of seconds with a smooth coating.

Example II A lead pattern may be introduced into the apparatus ofExample I in place of the aluminum disc.

The operation may be carried out in a similar manner, using nickecarbonyl sprayed into the chamber at a rate of about 2 /2 pounds ofliquid per minute.

In this operation the inert atmosphere may be hydrogen gas. The liquidmay be sprayed using hydrogen as the blasting gas, which gas is under apressure of 90 pounds per square inch and at a temperature of 200 F.

The lead pattern may be heated to a temperature of approximately 375 F.and in the presence of hydrogen the nickel carbonyl plated to a brightmetallic clean surface.

Example III A carbon steel plate AlSl-1020 may be introduced into thechamber of Example I and the process run under the following conditions:

The liquid supplied to the spray apparatus may be cobalt carbonyl. Theinert gas circulated in the chamber may be nitrogen from a sourcemaintained under a pressure slightly above atmospheric.

Temperature of the steel plate may be maintained at approximately 410 F.The cobalt carbonyl may be introduced at a liquid flow rate ofapproximately 4 pounds of carbonyl per minute.

In order to remove the decomposition products and the circulatingnitrogen, the gases are exhausted utilizing vacuum equipment capable ofmaintaining a pressure within the chamber of approximately 3 inches ofwater vacuum.

A smooth coating of cobaltmay be thus deposited on large plates in amatter of minutes.

Example IV Copper discs may be introduced into the chamber explained inconjunction with Example I and the process operated under the followingconditions:

Copper discs may be heated to approximately 380 F. The chamber may bepurged with hydrogen, and hydrogen gas may be used as the sprayingmedium. Antimony hydride may be introduced into the chamber through thespray apparatus at a rate of approximately 3 pounds per minute. Thesecopper discs of 3 inch diameter may be plated to a depth of .025 inchwith metallic antimony in a fraction of a minute.

It will be understood that while there have been given herein certainspecific examples of the apparatus and method of this invention, it isnot intended thereby to have this invention limited to or circumscribedby the specific details herein specified, in view of the fact that theapparatus of this invention may be modified according to individualpreference or conditions without necessarily departing from the spiritof this disclosure and the scope of the appended claim.

We claim:

Apparatus for plating objects by gaseous metal deposition, saidapparatus comprising an airtight chamber, a liquid atomizing meansdisposed in said chamber, said means including a nozzle comprising atubular member through which liquid to be atomized is introduced intosaid chamber, said tubular member being surrounded by an outer end fordischarging gas to propel a fine spray of liquid metal carbonyl intosaid chamber, means for supporting materials in said chamber and spacedfrom said nozzle for positioning material to be plated, means forheating said material which is arranged adjacent said material supportand remote from said nozzle, an inlet to said chamber for introducinginert gas and disposed at one end thereof, an outlet from said chamberfor removing inert gas and decomposition products from the chamberdisposed at the opposite end thereof, and blower means connected withsaid inlet for circulating inert gas through said chamber and at apressure above atmospheric.

References Cited in the file of this patent UNITED STATES PATENTS2,332,309 Drummond Oct. 19, 1943 2,453,141 Lange Nov. 9, 1948 2,508,509Germer et al. May 23, 1950 2,522,531 Mochel Sept. 19, 1950 2,576,289Fink Nov. 27, 1951 2,602,033 Lander July 1, 1952 2,619,433 Davis et a1Nov. 25, 1952 2,649,754 Davis et al. Aug. 25, 1953

